(a) Field of the Invention
The present invention relates to a butler matrix.
(b) Description of the Related Art
A butler matrix of a passive element is used in a multiple terminal amplifier to divide an input signal into N input signals or to combine N input signals with an output terminal. A micro-strip line, a strip line, a coaxial line, a wave guide, or others may be used in the butler matrix according to the amplitude of a signal. For the power distribution and power coupling, a 3 dB coupler is used in the butler matrix. Four 3 dB couplers are used in a 4×4 butler matrix and twelve 3 dB couplers are used in an 8×8 butler matrix.
However, the larger the degree of the butler matrix is, the larger the number of 3 dB couplers is, and thereby the path for connecting the couplers becomes more complicated and a part where transmission lines are crossed necessarily occurs. The crossed transmission lines have to be designed to be electrically or spatially separated.
For this purpose, there is a butler matrix of a structure in which micro-strip lines or strip lines are laminated. However, in this structure, a radio frequency (RF) signal of high power may not be transmitted through a transmission line such as the micro-strip lines or the strip lines.
Also, when a transmission line that is difficult to laminate such as a coaxial line or a wave guide is used, a 3-dimensional (3D) form of butler matrix is implemented by bending transmission lines that cross each other and by spatially separating them.
However, it is difficult to manufacture the 3D form of butler matrix and electrical loss may occur. In addition, if the degree of the butler matrix increases, the structure of the butler matrix becomes more complicated. This enlarges the volume of the butler matrix, and thereby it is difficult to manufacture the butler matrix.
Meanwhile, a planar type of butler matrix is implemented by electrically dividing signals in the part in which transmission lines are crossed with a 0 dB coupler. In this case, a phase difference between a transmission line with a 0 dB coupler and a transmission line without a 0 dB coupler occurs. Accordingly, an expensive phase shifter has to be used to compensate the phase difference.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.